1. Field of the Invention
The present invention relates to a light beam scanning system including light beam deflectors for scanning a recording medium with a two-dimensionally deflected light beam to record image information such as radiation image information on the recording medium or to read out such recorded image information from the recording medium.
1. Description of the Prior Art
There have been proposed various light beam scanning systems for use in image information recording and reading apparatus. In the image recording apparatus, a light beam such as a laser beam emitted from a light beam source is modulated by image information to be recorded, and a recording medium is two-dimensionally scanned by the modulated light beam to record the image information on the recording medium. In the apparatus for reading out image information, a light beam such as a laser beam two-dimensionally scans a recording medium storing image information to enable the recording medium to reflect, pass, or emit light representative of the stored image information. The light from the recording medium is then detected by a light detector such as a photomultiplier to produce an image signal indicating the stored image information. The apparatus for reading out image information is used, for example, in a scanner in the graphics arts field, a computer or facsimile input device, or a system for recording and reproducing radiation image information using a stimulable phosphor sheet, as proposed by the applicant in Japanese Unexamined Patent Publication Nos. 55(1980)-12429, 56(1981)-11395, and 56(1981)-11397, for example.
The image recording apparatus may preferably be connected to an apparatus for reading out radiation image information in such a system. The apparatus for reading out radiation image information operates by scanning a stimulable phosphor sheet that stores radiation image information with a stimulating light beam and photoelectrically reading light emitted from the stimulable phosphor sheet to produce an image signal. The image signal is applied to the image recording apparatus to produce a hard copy of good image quality for better image observation.
In the light beam scanning system, the light beam from the light beam source is deflected by a light beam deflector to scan the recording medium in a main scanning direction while the recording medium is being moved in an auxiliary scanning direction transverse to the main scanning direction, so that the recording medium can be scanned two-dimensionally by the light beam. However, conventional light beam scanning systems are disadvantageous in that they are large in size because of means required for moving the recording medium in the auxiliary scanning direction and they require a complex and expensive optical system.
One prior optical scanning system incorporated in an image recording apparatus will be described with reference to FIG. 62 of the accompanying drawings. A light beam 202 emitted from a light beam source 201 is applied to and modulated by a light modulator 203 which is driven by a modulator driver 204 based on an image signal from an image signal generator 205. The modulated light beam 202 is then applied to a light deflector 206 such as a rotating polygonal mirror by which the light beam 202 is cyclically reflected and deflected as the polygonal mirror 206 is rotated about its own axis in the direction of the arrow A. The light beam 202 reflected by the polygonal mirror 206 passes through an image-forming lens 207 such as an f .theta. lens to scan a sheet-like recording medium 208 in a main scanning direction indicated by the arrow B. The recording medium 208 is sandwiched between a drum 209 and a pair of pinch rollers 210A, 210B on the drum 209. As the drum 209 rotates in the direction of the arrow C, the recording medium 208 is moved in an auxiliary scanning direction indicated by the arrow D which is normal to the main scanning direction. The light beam 202 therefore scans the recording medium 208 repeatedly in the main scanning direction of the arrow B while the recording medium 208 is being moved in the auxiliary scanning direction of the arrow D. Thus, the recording medium 208 is two-dimensionally scanned to record image information on the recording medium 208 substantially over its entire surface.
The drum 209 is rotated in the direction of the arrow C by a motor 213 coupled thereto. To minimize any variations in the load on the motor 213 during movement of the recording medium 208 in the auxiliary scanning direction for eliminating irregularities in the image quality, the recording medium 208 is supported on support tables 211, 212 lying forwardly and rearwardly of the position where the recording medium 208 is scanned by the light beam 202. The support tables 211, 212 should be wide enough to support recording mediums, respectively, thereon. Therefore, the light beam scanning system must have a space to accommodate the support tables 211, 212 therein, and hence is large in size in the auxiliary scanning direction. The drum 209 has a width larger than that of the recording medium 208 for stably delivering the recording medium 208. Since the motor 213 is disposed in the axial direction of the drum 209, the light beam scanning system is also large in size in the main scanning direction.
To record desired image information highly accurately on the recording medium 208 while the latter is being transferred, the motor 213 must be controlled so that the recording medium 208 can be delivered at a constant speed with high accuracy. Inasmuch as the motor 213 that is controllable with high accuracy is expensive, the overall cost of the light beam scanning system is high. The rollers 210A, 210B required for stably feeding the recording medium 208 prevent any image from being recorded on the leading and trailing ends of the recording medium 208 in the auxiliary scanning direction. Consequently, the leading and trailing ends of the recording medium 208 cannot be processed into black edges, for example.
FIG. 63 shows another conventional light beam scanning system capable of scanning the recording medium in the auxiliary scanning direction without moving the recording medium. The light beam scanning system of FIG. 63 additionally includes an auxiliary scanning galvanometer mirror 220 angularly movable at a low speed in the direction of the arrow C for deflecting the light beam 202 to move the main scanning line in the direction of the arrow D over a sheet-like recording medium 219 which is fixed in position, while at the same time the light beam 202 is being deflected by the main scanning mirror 206 in the main scanning direction. The auxiliary scanning galvanometer mirror 220 completes its one angular movement in the direction of the arrow C normal to the main scanning direction while image information is being recorded on the recording medium 219. The recording medium 219 is thus two-dimensionally scanned with the light beam 202 by the main scanning mirror 206 and the auxiliary scanning galvanometer mirror 220. When the recording of image information on the recording medium 219 is finished, the auxiliary scanning galvanometer mirror 220 returns to its original position in readiness for a next cycle of recording image information. An image-forming lens 223 comprising an f.theta. lens is disposed between the auxiliary scanning galvanometer mirror 220 and the recording medium 219. The image-forming lens 223 serves to cause the light beam 202 which is reflected and deflected by the main and auxiliary mirrors 206, 220 at a constant angular velocity to linearly scan the flat recording medium 219 at a constant speed.
A relay lens 221 is disposed between the main and auxiliary scanning mirrors 206, 220 for enabling the path of the light beam 202 that has been spread by the main scanning mirror 206 to be converged onto the reflecting surface of the relatively small auxiliary scanning galvanometer mirror 220 and then for enabling the converged path of the light beam 202 to be spread from the auxiliary scanning galvanometer mirror 220. The auxiliary scanning galvanometer mirror 220 is positioned where the path of the light beam 202 is converged by the relay lens 221. Therefore, the light beam 202 is fully applied by the relay lens 221 to the auxiliary scanning galvanometer mirror 220 by which it is deflected. After the light beam 202 has been reflected and deflected by the auxiliary scanning galvanometer mirror 220, its path is spread thereby to the extent commensurate with the beam deflecting angle of the main scanning mirror 206, so that a main scanning line of required length can be formed on the recording medium 219.
With the light beam scanning system shown in FIG. 63, however, the optical system is complex making the entire scanning system large in size since the relay lens 221 is required in addition to the image-forming lens 223. Addition of the relay lens 221 increases the number of parts of the optical system and the cost thereof. The f.theta. lens 223 should be two-dimensionally improved in its characteristics inasmuch as the light beam 202 deflected by the main and auxiliary scanning mirrors 206, 220 is applied thereto over its substantially entire surface. The f.theta. lens 223 is therefore costly to manufacture, thus adding to the cost of the light beam scanning system.
FIG. 64 shows one conventional optical scanning system incorporated in an apparatus for reading out radiation image information. A stimulating light beam 302 of constant intensity emitted from a light beam source 301 is applied to a light deflector 303 comprising a galvanometer mirror and reflected and deflected thereby as it is angularly moved in the direction of the arrow A. The stimulating light beam 302 deflectd by the galvanometer mirror 303 then passes through an image-forming lens 104 comprising an f.theta. lens to scan a stimulable phosphor sheet 305 in a main scanning direction indicated by the arrow B. At the same time, the stimulable phosphor sheet 305 placed on an endless belt conveyor 306 is fed in the direction of the arrow D substantially normal to the main scanning direction. Therefore, the stimulable phosphor sheet 305 is two-dimensionally scanned over its entire surface by the stimulating light beam 302.
When exposed to the stimulating light beam 302, the stimulable phosphor sheet 305 emits light representing image information stored thereon, and the emitted light enters a transparent light guide 307 through an inlet end 307a extending parallel to the main scanning line closely to the stimulable phosphor sheet 305. The light guide 307 has a flat front end portion 307b positioned near the stimulable phosphor sheet 305 and progressively narrowed into a cylindrical rear end portion 307c which is coupled to a photomultiplier 308. Therefore, the light that has entered the light guide 307 is applied through the rear end portion 307c to the photomultiplier 308, which includes a filter for rejecting extraneous light other than the light emitted from the stimulable phosphor sheet 305. The applied light is photoelectrically converted by the photomultiplier 308 to an electric signal that is processed by an image information reading circuit 309. The processed signal is displayed as a visible image on a CRT 310, recorded on a magnetic tape 111, or recorded on a photographic photosensitive sheet to produce a hard copy.
Since the stimulable phosphor sheet 305 is moved for auxiliary scanning, the endless belt conveyor 306 must be of such a size as to allow at least two stimulable phosphor sheets to be placed thereon forwardly and rearwardly of the scanning position. The endless belt conveyor 306 thus has a length corresponding to at least two stimulable phosphor sheets in the auxiliary scanning direction, making the optical beam scanning system large in size.
Prior to reading out the stored radiation image information (main reading mode) for image display or recording purpose, the stored radiation image information may roughly be read out (preliminary reading mode) to determine read-out conditions based on which the main reading mode will be carried out. According to Japanese Unexamined Patent Publication No. 58(1983)-67240, such a preliminary reading mode is effected by scanning the stimulable phosphor sheet with stimulating light of a lower energy than that of stimulating light used in the main reading mode, and photoelectrically reading light emitted from the stimulable phosphor sheet upon exposure to the lower-energy stimulating light.
For effecting the main and preliminary reading modes successively, the stimulable phosphor sheet 305 is fed in the direction of the arrow D in the preliminary reading mode, and then the endless belt conveyor 306 is reversed to deliver the stimulable phosphor sheet 305 backwards in the direction of the arrow D'. Thereafter, the stimulable phosphor sheeet 305 is fed again in the direction of the arrow D in the main reading mode. Alternatively, after the stimulable phosphor sheet 305 is fed in the direction of the arrow D in the preliminary reading mode, it is moved back in the direction of the arrow D' while the main reading mode is being carried out, followed by discharging the stimulable phosphor sheet 305 in the direction of the arrow D. However, inasmuch as the stimulable phosphor sheet 305 is required to be fed back and forth in the main and preliminary reading modes, and hence a time required for the main and preliminary reading modes is long, failing to achieve an efficient reading process.
FIG. 65 shows a proposed apparatus for reading out radiation image information, which has a light source 301A energizable for the preliminary reading mode and another light source 302A energizable for the main reading mode. The main and prelimiary reading modes can successively be effected by delivering a stimulable phosphor sheet in the direction of the arrows E by a series of endless belt conveyors 309A, 309B, 309C, 309D, 309E without moving back the stimulable phosphor sheet. The conveyor system however requires a length corresponding to at least three stimulable phosphor sheets in the auxiliary scanning direction, with the result that the entire apparatus is larger in size.
For reading out radition image information highly accurately, a motor or motors for the endless belt conveyors must be controlled so that the stimulable phosphor sheet can be delivered at a constant speed with high accuracy even if subjected to load variations. Such a motor or motors are expensive, and the overall cost of the light beam scanning system is high.